Individuals with stroke and cerebral palsy have impaired movement and coordination which hinders activities of daily living and negatively impacts quality of life. Rehabilitation research has demonstrated that repetitive practice can improve function; however, the methods to support this practice are time and resource intensive and largely remain in laboratories and specialized clinics. Advances in sensor technology and ubiquitous computing have created new pathways to understand and monitor human activity during daily life and thus facilitate movement practice in the home and community. The objective of the proposed research is to develop the technology to enable ubiquitous rehabilitation - rehabilitation that harnesses activities of daily life to monitor, train, and improve movement. Specifically, this proposal outlines a 4-year, multidisciplinary research agenda to design, develop, and evaluate novel approaches for tracking and training muscle activity to improve upper extremity function for individuals with stroke and cerebral palsy. This research will combine expertise in engineering, material science, and rehabilitation to achieve three primary objectives to: (1) Further develop and test novel stretchable, wireless electromyography sensors for muscle activity monitoring and mobile interfaces for data processing, visualization, and biofeedback training, (2) Quantify the magnitude and complexity of muscle activity during daily life in both unimpaired individuals and individuals with stroke and cerebral palsy, and (3) Evaluate the plasticity of muscle activity in response to biofeedback training integrated into dail life. The results of this research will expand our understanding of how humans control movement in daily life and create new pathways to enhance movement and reduce the burdens of rehabilitation after neurologic injury.